Nitrate Upcycling Mediated by Organonickel Catalysis.

Nitrogen oxides (NO) are major environmental pollutants and to neutralize this long-term environmental threat, new catalytic methods are needed. Although there are biological denitrification processes involving four different enzymatic reactions to convert nitrate (NO ) into dinitrogen (N), it is unfortunately difficult to apply in industry due to the complexity of the processes. In particular, nitrate is difficult to functionalize because of its chemical stability.

Hydrosulfonylation of Alkynes for Stereodivergent Synthesis of Vinyl Sulfones: Synthetic Strategy and Mechanistic Insights.

Direct synthesis of thermodynamically less favorable ()-vinyl sulfones presents a notable challenge in organic synthesis. In addition, the development of a stereodivergent synthesis for ()- and ()-vinyl sulfones is crucial but remains elusive. In this study, we present a hydrosulfonylation of aryl-substituted alkynes, achieving a stereodivergent synthesis of ()- and ()-vinyl sulfones by leveraging both thermodynamic and kinetic controls.

Strong intramolecular charge-transfer effect strengthening naphthoquinone-based chemosensor: Experimental and theoretical evaluation.

An aminophenol-linked naphthoquinone-based fluorometric and colorimetric chemosensor 2-chloro-3-((3-hydroxyphenyl) amino) naphthalene-1,4-dione (2CAN-Dione) was synthesized for selective detection of Sn ion in aqueous solution. The amine and conversion of carbonyl into carboxyl groups play a vital role in the sensing mechanism when Sn is added to 2CAN-Dione. Comprehensive characterization of the sensor was carried out using standard spectral and analytical approaches.

"Lighting up" fluoride: cellular imaging and zebrafish model interrogations using a simple ESIPT-based mycophenolic acid precursor-based probe.

The discovery and implementation of media that derive from bioinspired designs and bear optical readouts featuring large Stokes shifts are of continued interest to a wide variety of researchers and clinicians. Myco-F, a novel mycophenolic acid precursor-based probe features a cleavable -butyldimethylsiloxy group to allow for fluoride detection. Myco-F exhibits high selectivity and specificity towards F (Stokes shift = 120 nm).

A Manganese Compound I Model with a High Reactivity in the Oxidation of Organic Substrates and Water.

A high-valent manganese(IV)-hydroxo porphyrin π-cation radical complex, [Mn(IV)(OH)(Porp)(X)], was synthesized and characterized spectroscopically. The Mn porphyrin intermediate was highly reactive in alkane hydroxylation and oxygen atom transfer reactions. More importantly, the Mn porphyrin intermediate reacted with water at a fast rate, resulting in the dioxygen evolution.

Electronic Effect on Phenoxide Migration at a Nickel(II) Center Supported by a Tridentate Bis(phosphinophenyl)phosphido Ligand.

A phosphide nickel(II) phenoxide pincer complex () reacts with CO(g) to give a pseudo-tetrahedral nickel(0) monocarbonyl complex () possessing a phosphinite moiety. This metal-ligand cooperative (MLC) transformation occurs with a (PPP)Ni scaffold (PPP = P[2-PPr-CH]), which can accommodate both square planar and tetrahedral geometries. The 2-electron reduction of a nickel(II) species induced by CO coordination involves group transfer to generate a P-O bond.

Two-Electron-Induced Reorganization of Cobalt Coordination and Metal-Ligand Cooperative Redox Shifting Co(I) Reactivity toward CO Reduction.

Electrochemical reorganization of complex structures is directly related to catalytic reactivity; thus, the geometric changes of catalysts induced by electron transfer should be considered to scrutinize the reaction mechanism. Herein, we studied electron-induced reorganization patterns of six-coordinate Co complexes with neutral N-donor ligands. Upon two-electron transfer into a Co center enclosed within a bulky π-acceptor ligand, the catalytic site exhibited different reorganization patterns depending on the ligand characteristics.

Heme compound II models in chemoselectivity and disproportionation reactions.

Heme compound II models bearing electron-deficient and -rich porphyrins, [Fe(O)(TPFPP)(Cl)] (1a) and [Fe(O)(TMP)(Cl)] (2a), respectively, are synthesized, spectroscopically characterized, and investigated in chemoselectivity and disproportionation reactions using cyclohexene as a mechanistic probe. Interestingly, cyclohexene oxidation by 1a occurs at the allylic C-H bonds with a high kinetic isotope effect (KIE) of 41, yielding 2-cyclohexen-1-ol product; this chemoselectivity is the same as that of nonheme iron(iv)-oxo intermediates. In contrast, as observed in heme compound I models, 2a yields cyclohexene oxide product with a KIE of 1, demonstrating a preference for C[double bond, length as m-dash]C epoxidation.

An end-on bis(μ-hydroxido) dimanganese(II,III) azide complex for C-H bond and O-H bond activation reactions.

We report the synthesis of an end-on dinuclear Mn(II) azide complex with two bridging azide ligands that served as a precursor for the formation of an end-on bis(μ-hydroxido) dinuclear Mn(II,III) azide complex upon oxidation by organic peroxide or peracids. Combined experimental and theoretical studies on the reactivity of the end-on bis(μ-hydroxido) dinuclear Mn(II,III) azide complex suggest that the reaction with substrates having weak C-H bond and O-H bond dissociation energy occurred a H-atom abstraction reaction in a concerted manner.

Structure and Reactivity of Nonporphyrinic Terminal Manganese(IV)-Hydroxide Complexes in the Oxidative Electrophilic Reaction.

High-valent transition metal-hydroxide complexes have been proposed as essential intermediates in biological and synthetic catalytic reactions. In this work, we report the single-crystal X-ray structure and spectroscopic characteristics of a mononuclear nonporphyrinic Mn-(OH) complex, [Mn(Me-TPADP)(OH)(OCHCH)] (), using various physicochemical methods. Likewise, [Mn(Me-TPADP)(OH)(OCHCF)] (), which is thermally stable at room temperature, was also synthesized and characterized spectroscopically.

Nickel-Catalyzed NO Group Transfer Coupled with NO Conversion.

Nitrogen oxide (NO) conversion is an important process for balancing the global nitrogen cycle. Distinct from the biological NO transformation, we have devised a synthetic approach to this issue by utilizing a bifunctional metal catalyst for producing value-added products from NO. Here, we present a novel catalysis based on a Ni pincer system, effectively converting Ni-NO to Ni-NO via deoxygenation with CO(g).

Mono- and dinuclear zinc complexes bearing identical bis(thiosemicarbazone) ligand that exhibit alkaline phosphatase-like catalytic reactivity.

Mono- and dinuclear zinc(II) complexes bearing bis(thiosemicarbazone) (bTSC) ligand were employed in the cleavage of phosphoester bonds. Comparative kinetic studies combined with theory suggested that the P-O bond cleavage is much accelerated by dinuclear zinc(II) complex in the presence of base. Based on the DFT-optimized structures of the proposed intermediates, it is plausible that (1) the removal of sulfur atoms of bTSC ligand from the zinc center provides two vacant sites for the binding of water (or hydroxide ion) and phosphoester and (2) the H-bonding between water (or hydroxide ion) and phosphoester, through several water molecules, may also assist the P-O bond cleavage and facilitate the nucleophilic attack.

Nonheme Iron Imido Complexes Bearing a Non-Innocent Ligand: A Synthetic Chameleon Species in Oxidation Reactions.

High-valent iron-imido complexes can perform C-H activation and sulfimidation reactions, but are far less studied than the more ubiquitous iron-oxo species. As case studies, we have looked at a recently published iron(V)-imido ligand π-cation radical complex, which is formally an iron(VI)-imido complex [Fe (NTs)(TAML )] (1; NTs=tosylimido), and an iron(V)-imido complex [Fe (NTs)(TAML)] (2). Using a theoretical approach, we found that they have multiple energetically close-lying electromers, sometimes even without changing spin states, reminiscent of the so-called Compound I in Cytochrome P450.

Metal-ligand cooperative transformation of alkyl azide to isocyanate occurring at a Co-Si moiety.

A cobalt-silyl moiety reveals metal-ligand cooperative group transfer to generate isocyanate from the reaction of alkyl azide and CO. This reaction involves the reversible insertion of a nitrene group into a Co-Si bond. Photolysis leads to ligand substitution of a Co(CO) species, allowing the successful catalytic conversion of AdN to AdNCO under CO(g).

Ligand Architecture Perturbation Influences the Reactivity of Nonheme Iron(V)-Oxo Tetraamido Macrocyclic Ligand Complexes: A Combined Experimental and Theoretical Study.

Iron(V)-oxo complexes bearing negatively charged tetraamido macrocyclic ligands (TAMLs) have provided excellent opportunities to investigate the chemical properties and the mechanisms of oxidation reactions of mononuclear nonheme iron(V)-oxo intermediates. Herein, we report the differences in chemical properties and reactivities of two iron(V)-oxo TAML complexes differing by modification on the "Head" part of the TAML framework; one has a phenyl group at the "Head" part (), whereas the other has four methyl groups replacing the phenyl ring (). The reactivities of and in both C-H bond activation reactions, such as hydrogen atom transfer (HAT) of 1,4-cyclohexadiene, and oxygen atom transfer (OAT) reactions, such as the oxidation of thioanisole and its derivatives, were compared experimentally.

Mechanistic dichotomies in redox reactions of mononuclear metal-oxygen intermediates.

There are mechanistic dichotomies with regard to the formation, electronic structures and reaction mechanisms of metal-oxygen intermediates, since these metal-oxygen species could be composed of different resonance structures or canonical structures of the oxidation states of metals and ligands, which may undergo different reaction pathways. Even the same metal-oxygen intermediates, such as metal-oxo species, may undergo an electron-transfer pathway or a direct hydrogen or oxygen atom transfer pathway depending on the one-electron redox potentials of metal-oxo species and substrates. Electron-transfer pathways are also classified into two mechanisms, such as outer-sphere and inner-sphere pathways.

Electron-Transfer and Redox Reactivity of High-Valent Iron Imido and Oxo Complexes with the Formal Oxidation States of Five and Six.

We report for the first time electron-transfer (ET) properties of mononuclear nonheme iron-oxo and -imido complexes with the formal oxidation states of five and six, such as an iron(V)-imido TAML cation radical complex, which is formally an iron(VI)-imido complex [Fe(NTs)(TAML)] (; NTs = tosylimido), an iron(V)-imido complex [Fe(NTs)(TAML)] (), and an iron(V)-oxo complex [Fe(O)(TAML)] (). The one-electron reduction potential ( vs SCE) of was determined to be 0.86 V, which is much more positive than that of (0.

High-Spin Mn(V)-Oxo Intermediate in Nonheme Manganese Complex-Catalyzed Alkane Hydroxylation Reaction: Experimental and Theoretical Approach.

Mononuclear nonheme manganese complexes are highly efficient catalysts in the catalytic oxidation of hydrocarbons by hydrogen peroxide in the presence of carboxylic acids. Although high-valent Mn(V)-oxo complexes have been proposed as the active oxidants that afford high regio-, stereo-, and enantioselectivities in the catalytic oxidation reactions, the importance of the spin state (e.g.

A mononuclear manganese(iii)-hydroperoxo complex: synthesis by activating dioxygen and reactivity in electrophilic and nucleophilic reactions.

We report the synthesis of manganese(iii)-peroxo (Mn(O)) and manganese(iii)-hydroperoxo (Mn(OH)) complexes by activating dioxygen (O) and the amphoteric reactivity of the Mn(iii)-hydroperoxo complex in electrophilic and nucleophilic reactions.

Structure and spin state of nonheme FeO complexes depending on temperature: predictive insights from DFT calculations and experiments.

The spin states ( = 1 and = 2) of nonheme FeO intermediates are believed to play an important role in determining their chemical properties in enzymatic and biomimetic reactions. However, it is almost impossible to investigate the spin state effect of nonheme FeO species experimentally, since FeO models having the = 1 and = 2 spin states at the same time neither exist nor can be synthesized. However, recent synthesis of an FeO complex with an = 1 spin state (triplet), [(MeNTB)FeO] (), and a structurally similar FeO complex but with an = 2 spin state (quintet), [(TQA)FeO] (), has allowed us to compare their reactivities at 233 K.

Mutable Properties of Nonheme Iron(III)-Iodosylarene Complexes Result in the Elusive Multiple-Oxidant Mechanism.

Although nonheme iron(III)-iodosylarene complexes present amazing oxidative efficiency and selectivity, the nature of such complexes and related oxidation mechanism are still unsolved after decades of experimental efforts. Density functional calculations were employed to explore the structure-reactivity relationship of the iron(III)-iodosylbenzene complex, [Fe(tpena) (PhIO)] (1), in thioanisole sulfoxidation. Our theoretical work revealed that complex 1 can evolve into two resonance valence-bond electronic structures (a high-valent iron-oxo species and a monomeric PhIO species) in thioanisole sulfoxidation to present different reaction mechanisms (the novel bond-cleavage coupled electron transfer mechanism or the direct oxygen-atom transfer mechanism) as a response to different substrate attack orientations.

Synthesis and reactivity of a mononuclear non-haem cobalt(IV)-oxo complex.

Terminal cobalt(IV)-oxo (Co-O) species have been implicated as key intermediates in various cobalt-mediated oxidation reactions. Herein we report the photocatalytic generation of a mononuclear non-haem [(13-TMC)Co(O)] (2) by irradiating [Co(13-TMC)(CFSO)] (1) in the presence of [Ru(bpy)], NaSO, and water as an oxygen source. The intermediate 2 was also obtained by reacting 1 with an artificial oxidant (that is, iodosylbenzene) and characterized by various spectroscopic techniques.

Tunneling Effect That Changes the Reaction Pathway from Epoxidation to Hydroxylation in the Oxidation of Cyclohexene by a Compound I Model of Cytochrome P450.

The rate constants of the C═C epoxidation and the C-H hydroxylation (i.e., allylic C-H bond activation) in the oxidation of cyclohexene by a high-valent iron(IV)-oxo porphyrin π-cation radical complex, [(TMP)Fe(O)(Cl)] (1, TMP = meso-tetramesitylporphyrin dianion), were determined at various temperatures by analyzing the overall rate constants and the products obtained in the cyclohexene oxidation by 1, leading us to conclude that reaction pathway changes from the C═C epoxidation to C-H hydroxylation by decreasing reaction temperature.

Intermetal oxygen atom transfer from an FeO complex to a Mn complex: an experimental and theoretical approach.

Oxygen atom transfer (OAT) reaction between an FeO complex and a Mn complex resulted in the eventual formation of their corresponding Fe and MnO complexes. The reaction proceeded via an initial fast OAT reaction between the FeO and Mn complexes, yielding a half equivalent of a MnO complex and a μ-oxo bridged Fe dimer. The dimer regenerated the FeO species via equilibrium, which then reacted with the remaining Mn complex to produce another half equivalent of the MnO complex.

Mechanistic Insight into the Nitric Oxide Dioxygenation Reaction of Nonheme Iron(III)-Superoxo and Manganese(IV)-Peroxo Complexes.

Reactions of nonheme Fe(III) -superoxo and Mn(IV) -peroxo complexes bearing a common tetraamido macrocyclic ligand (TAML), namely [(TAML)Fe(III) (O2 )](2-) and [(TAML)Mn(IV) (O2 )](2-) , with nitric oxide (NO) afford the Fe(III) -NO3 complex [(TAML)Fe(III) (NO3 )](2-) and the Mn(V) -oxo complex [(TAML)Mn(V) (O)](-) plus NO2 (-) , respectively. Mechanistic studies, including density functional theory (DFT) calculations, reveal that M(III) -peroxynitrite (M=Fe and Mn) species, generated in the reactions of [(TAML)Fe(III) (O2 )](2-) and [(TAML)Mn(IV) (O2 )](2-) with NO, are converted into M(IV) (O) and (.) NO2 species through O-O bond homolysis of the peroxynitrite ligand.